Methlyene Blue

Methylene blue is employeed as an antidote for poisonings that cause
methemoglobin formation (such as nitrites). The antidote for cyanide
poisoning involves the purposeful induction of methemoglobin , but short
of causing serious depression of the O2-carrying ability of blood. By
doing this the cyanide bound to ferric ions of critical cytochrome
enzymes of the electron transport chain are eventually equilibrated with
the ferric ions of methemoglobin. The binding of cyanide to cytochrome
is the potentially lethal event of cyanide poisoning and must be
reversed. Since the total pool of iron is much larger in blood than the
total iron present in the critical cytochromes, it is possible to shift
the equilibrium binding of cyanide out of the mitochondria (which is the
site of the electron transport chain and the cytochrome coenzymes) into
hemoglobin {but only for the oxidized form known as methemoglobin in
which iron is Fe(3); normal hemoblobin has iron as Fe(2)}. At this
point treatment then involves conversion of the
cyanide-bound-to-Hemoglobin into thiocyanate which is nontoxic and
readily excreted. This of course being achieved with thiosulfate. The
only possible use of methylene blue in cyanide treatment would be to
remove excess methemoglobin once the cyanide problem has been corrected.
Michael Corbett, Ph.D.
Independent Consultant
Omaha, NE